1. Field of the Invention
The present invention generally relates to atomic layer deposition (ALD) technology, particularly to a method for forming a film by ALD which controls film growth in a vertical direction.
2. Description of the Related Art
Basically, Atomic Layer Deposition (ALD) is implemented by repeating a process of oxidizing, by means of plasma decomposition reaction or thermal reaction in an oxygen atmosphere, a material adsorbed onto a substrate. This ALD is largely classified into two types based on the oxidization method. To be specific, the type of ALD that uses plasma decomposition reaction of oxygen is called “Plasma Enhanced ALD (PE-ALD),” while the other type of ALD that uses thermal reaction in an oxygen ambience is called “Thermal ALD.”
In ALD, a film grows more gradually than when PE-CVD is used. However, ALD is characterized in that, because the material which has been adsorbed onto the substrate as an atomic layer is oxidized without fail, the carbon content originating from the material is kept to a minimum even when the film forming temperature is low and that the resulting amorphous film also contains fewer methyl groups, hydoroxy groups, hydrogen and other terminal groups originating from the material. In addition, ALD is characterized in that, by use of the saturated adsorption of the material, an in-plane uniformity of less than 1% and step coverage of 100% can be achieved easily.
If this ALD is applied to a gap filling, side wall spacer or spacer-defined double patterning (SDDP), however, the 100% step coverage will present problems, although such application is very effective in terms of film quality and in-plane uniformity.
Take a gap filling, for example. ALD will present the above problems when patterns of different pitches are buried uniformly. If wide-pitch patterns are buried by means of ALD until their surface becomes flat, excessive film will deposit on top of narrow-pitch patterns. For this reason, chemical & mechanical polishing (CMP) or dry etching must be implemented in a subsequent process to remove the film deposited on top. The same applies to side wall spacer and SDDP, where the film on top that has grown as thick as the film on side walls must be removed by CMP or dry etching. To eliminate this subsequent process of CMP or dry etching, a film growth in a vertical direction must be controlled.
As for PE-CVD, a technology for film growth in a selected direction, which is called “Flowable CVD,” is available, but no such direction-selective film growth technology is available in the case of ALD. To widen the scope of application of ALD, development of direction-selective film growth technology is desired.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.